Netgear VPN/Firewall issue

I've been asked to upgrade my neighbour's network. They are upgrading their current switch to a Netgear Prosafe FVS318G, which sits between their router and the devices they want to protect for their small business. The consoles etc. will go directly to the router.

I've followed every instruction in the book, and I can't get this thing to work. The network simply won't pick it up & neither the router nor the computers acknowledge it exists. I've

• run through set-up three times,
  
• tried scanning the network to see if anything detects it (no),
  
• plugged things directly into the router to check the router is live (it is)
  
• checked to make sure the router and Netgear aren't on conflicting IPs, (they aren't - in fact as far as the network is concerned the Netgear doesn't have an IP).
  
• Factory reset didn't change a thing.
  
• Tried it with different OS's, no luck, and
  
• even checked the router's security isn't interfering. Turns out it really doesn't have much in the way of security which is why they want the firewall.

Netgear's own support either want to charge £50 to ask them if it's broken, or register it so I can't return it before they'll tell me if it's broken. Does anyone have any experience with this Netgear router, or suggestions on how to fix the thing? I normally use Cisco or SMC (running one at the moment), and they tend to be detected fairly easily.